Use of a borescope to determine the sex and egg maturity stage of sturgeons and the effect of borescope use on reproductive structures

During telemetry studies on Connecticut River shortnose sturgeon Acipenser brevirostrum, we used a 16-mm long fiberoptic borescope inserted into the genital canal to see eggs and identify females and egg stage. The procedure lasted 1-2 min and enabled us to selectively identify females of any season. Of 443 adults examined during 6 years, 174 were classified as females: 90 with late-stage eggs ( mature the next spawning period), 80 with early-stage eggs ( not mature the next spawning period), and four had eggs of unknown egg stage. Sex of the remaining 270 sturgeon could not be determined ( either females with immature eggs or males). Using the borescope, a re-examination of 21 recaptured fish originally classified as females found the sex of all had been correctly identified. Examination of shortnose sturgeon and juveniles of three other sturgeon species indicated that the urinogenital opening diameter, not the genital canal diameter, determines the largest diameter borescope that can be used. Repeated probing of the oviduct valve by 4-mm and smaller diameter probes did not penetrate the valve regardless of species or fish length, showing borescope use will not damage the valve. Careful use of a borescope will not harm reproductive structures and is suitable for all sturgeon species.